The present invention relates to an overdrive amplifier and a semiconductor device including the same, and it further relates to a technique useful in application to e.g. a drive IC (Integrated Circuit) of LCD (liquid crystal display).
The load-driving performance of a drive amplifier such as a buffer amplifier varies between near and far ends of a load and changes depending on the temperature of the load. For instance, in a liquid crystal display panel, liquid crystal display elements are arrayed in row and column directions like a matrix; gate lines are connected to liquid crystal display element select terminals in units of display lines along the row direction, and source lines are connected to liquid crystal display element data terminals in units of columns along the column direction. In such a display panel, a drive amplifier drives source lines each time a display line is selected. In the source lines, resistance components and liquid crystal display elements' capacitance components are distributed; a load component becomes larger at a farther end. Even if a drive amplifier is caused to work at a high speed, a near end of a load is shorter in convergence time, but it is different from a far end of the load in convergence time under the influence of a panel load, and the far end tends to be late in convergence time. In the case of a large panel load, RC of the panel load becomes dominant in the convergence time at a far end of each load. Therefore, even if the drive amplifier is sped up, it is difficult to achieve a high speed beyond the limitation.
The difference between near and far ends of a load in convergence time in driving comes to the surface depending on the size of a liquid crystal display panel, the quantity of its allowable power consumption, etc. In addition, the difference can arise under a low-temperature environment.
In regard to such difference in convergence time in driving, an overdrive processing to cope with the problem has been known, which is disclosed in e.g. the Japanese Unexamined Patent Application Publication No. JP-A-2006-47767. In the overdrive processing, in the event of change in display gradation, an attempt is made to improve the speed of driving a drive amplifier by activating liquid crystal with drive data which results from the addition of a correction value depending on the quantity of the change to a gradation value concerned. Further, there is a description about an overdrive controller in JP-A-2003-29713, which produces an overdrive voltage for overdrive processing under the control of a logic circuit.